The Server Time Protocol feature is designed to provide the capability for multiple servers and Coupling Facilities to maintain time synchronization with each other, without requiring a Sysplex Timer. The servers and Coupling Facilities that are capable of supporting Server Time Protocol are the z890, z990, and later servers.
Server Time Protocol is a server-wide facility that is implemented in the Licensed Internal Code (LIC) and presents a single view of time to Processor Resource/Systems Manager™ (PR/SM™). STP uses a message-based protocol in which timekeeping information is passed over externally defined Coupling Links - InterSystem Channel-3 (ISC-3) links configured in peer mode, Integrated Cluster Bus-3 (ICB-3) links, Integrated Cluster Bus-4 (ICB-4) links. and Parallel Sysplex InfiniBand (PSIFB) links. These can be the same links that already are being used in a Parallel Sysplex for Coupling Facility (CF) message communication.
By using the same links to exchange timekeeping information and Coupling Facility messages in a Parallel Sysplex, STP can scale with distance. Servers exchanging messages over short distance links such as ICB-3 and ICB-4 are designed to meet more stringent synchronization requirements than servers exchanging messages over long distance links such as ISC-3 (distances up to 100 km, longer distances possible with RPQ 8P2263), where the synchronization requirements are less stringent. This is an enhancement over the current Sysplex Timer implementation, which does not scale with distance.
The STP design has introduced a new concept called Coordinated Timing Network (CTN). A Coordinated Timing Network (CTN) is a collection of servers and Coupling Facilities that are time synchronized to a time value called Coordinated Server Time.
STP supports the following functions:
- Initialize the time manually or by dialing out to a time service, so that Coordinated Server Time can be set to within 100 milliseconds of an international time standard such as Coordinated Universal Time (UTC).
- Schedule periodic dial-outs to a time service so that Coordinated Server Time may be gradually steered to an international time standard.
- Initialize Time Zone offset, Daylight Saving Time (DST) offset, Leap seconds offset.
- Schedule changes to offsets listed above. STP can automatically schedule Daylight Saving Time, based on the selected Time Zone, a capability that did not exist on the Sysplex Timer.
- Adjust Coordinated Server Time by up to +/- 60 seconds. This improves upon the Sysplex Timer's capability of adjusting time by up to +/- 4.999 seconds.
Please see the STP Hardware announcement 106-715 Server Time Protocol for IBM System z9, zSeries 990 and 890; non-raised-floor support for System z9 BC dated October 10, 2006 or download (PDF, 67KB) the pdf version.
STP FAQs can be seen at:
The Server Timer Protocol feature is designed to simplify hardware configurations by:
- Allowing clock synchronization for supported servers and Coupling Facilities without requiring the Sysplex Timer and dedicated timer links. This helps reduce the need for separate hardware that needs to be ordered and maintained.
- Supporting a multisite timing network of up to 100 km (62 miles) over fiber optic cabling, thus allowing a sysplex to span these distances. This overcomes the limitations of the Sysplex Timer to Sysplex Timer links being supported only up to 40 km. STP is designed to eliminate the need for a third site to locate the second Sysplex Timer for installations where the multisite sysplex spans a distance greater than 40 km but less than 100 km (the current limit for Sysplex Timer to server connection). Distances over 100 km may be possible with RPQ 8P2263.
- Potentially reducing the cross-site connectivity required for a multisite Parallel Sysplex. Dedicated links are no longer required to transport timing information since STP and Coupling Facility messages may be transmitted over the same links.
Additional value from Server Time Protocol may be obtained by:
- Eliminating infrastructure requirements (space, power, etc) needed to support Sysplex Timers
- Eliminating Sysplex Timer maintenance costs
- Eliminating fiber optic infrastructure requirements for:
- Patch/trunk cables
- Dense Wavelength Division Multiplexer (DWDM) ports
- Dark fiber between sites for External Time Reference (ETR) and Control Link Oscillator (CLO) links (links between Sysplex Timers)
Concurrent Migration and Coexistence
STP introduces the concept of a Coordinated Timing Network (CTN), to meet two key goals of System z customers:
- Concurrent migration from an existing External Time Reference (ETR) network to a timing network using STP.
- Capability of servers that cannot support STP to be synchronized in the same network as servers that support STP (z9 EC, z9 BC, z990, z890)
A CTN can be configured in two ways:
- Mixed CTN (ETR and STP) which requires a Sysplex Timer. The Sysplex Timer provides the timekeeping information in a Mixed CTN.
A Mixed CTN allows you to meet the above requirements of concurrent migration and coexistence. The coexistence allows for a sysplex configuration where members of the sysplex may reside on a z800 or z900 server.
- STP-only CTN which does not require a Sysplex Timer.